Longifolene, C15H24 (decahydro-4,8,8-trimethyl-9-methylene-1-4-methanoazulene), is present in the Indian turpentine oil obtained from Chirpine (Pinus longifolia) to the extent of 5–7%. This is the largest tonnage sesquiterpene hydrocarbon available anywhere in the world.
The economical utilization of this terpene hydrocarbon involves its transformation into isomeric product iso-longifolene and its derivatives, which have extensively used in perfumery industry due to their woody and floral odor. The acid catalysed and hydroformylated products of this isomerized iso-longifolene (2,2,7,7-tetramethyltricyclo undec-5-ene) have also woody amber odor and are used as a flavor in many pharmaceutical industries.
This isomerized aromatic compound is of commercial importance in pharmaceutical industries as a flavor. Presently, iso-longifolene, C15H24, is mainly produced by a rearrangement of longifolene involving a number of steps catalysed by mineral acids like sulfuric acid/acetic acid. Currently used processes using mineral acids is a multi-step process which results into a large quantity of unwanted-waste chemicals as by-products that requires further treatment before disposal.
The use of hazardous mineral acid is not safe from handling point of view, as they are corrosive, irritant and also required in more than stoichiometric amount. Furthermore, isomerized product obtained using mineral acid possesses some colour due to impurities generated, which needs further purification.
Therefore, research efforts to prepare iso-longifolene from longifolene to overcome the above-mentioned disadvantages and to find an eco-friendly and safer catalyst are needed.

Reference is made to Sobti, R R and Dev, S. (Tetrahedron, Volume 26, 649, 1970) who have reported synthesis of isolongifolene from camphene-1-carboxylic acid using multi-step process. Besides involving many steps, this route has a drawback in producing a by-product C13-keto acid, which is produced due to degradation of isolongifolene and uses reagents in stoichiometric amounts.
Prablad, J. R. et al. (Tetrahedron Letters, Volume 60, 417, 1964), who have reported the synthesis of isolongifolene from acid catalysed hydration of longifolene using acid treated silica gel. This synthesis strategy has a major drawback in the stability of the catalysts used as leaching of acid occurs from silica gel with prolonged use.
Beyler, R. E. and Ourisson, G. (J. Org. Chem. Volume 30, 2838, 1965) who have reported the synthesis of isolongifolene by treating longifolene with boron trifluoride etherate. In a typical reaction, longifolene is taken in sodium-dried ether to which boron trifluoride etherate is added and the mixture is refluxed on a steam bath for 60 minutes. Resultant dark brown mixture is added cautiously to excess of potassium hydroxide and ice. The mixture is stirred at ambient temperature for 90 minutes at the end of which the ether phase becomes straw yellow in colour. Separation and further extraction, water wash and, evaporation of ether result into light yellow isolongifolene. This route has drawback of using multi step synthesis of isolongifolene using hazardous chemicals like KOH, BF3 and sodium metal. Separation of the product from the reaction mixture imbibes several chemical treatments and is additionally time consuming before product can be obtained.
Bisarya S. C. et al. (Tetrahedron Letters Volume 28, 2323, 1969) reports the synthesis of isolongifolene by treating longifolene with amberlyst-15 (Rohm and Haas) or acid treated silica gel at 95° C. for 36 hours with 95% yield of isolongifolene. This process has drawback in using amberlyst, ion exchange resin, which have poor thermal stability and also swell with prolonged use. Furthermore, the process takes 36 hours for completion.
Ramesha A. R. et al. (Organic Preparation Procedure International, Volume 31, 227, 1999) have reported the isomerization of longifolene using montmorillonite clay K10 at 120° C. with 100% selectivity and more than 90% conversion. However, the process has drawback in using natural clays which have lot of impurities and difficult to reproduce with the requisite surface acidity. Furthermore, the thermal stability of the clays is low and these get deactivated with use and regeneration and re-usability of the clay catalyst is not known.
Kula J., and Masarweh A. (Flavour and Fragrance Journal, Volume 13, 277, 1998) have reported acid catalyzed rearrangement of longifolene to isolongifolene using bromoacetic acid. This process has drawback in using liquid bromoacetic acid for isomerization, which is not safe to handle. Moreover, the separation of the product from the reaction mixture is difficult.
Nayak, U. R. and Dev S. (Tetrahedron, 8, 42, 1960) have reported the preparation of isolongifolene by hydration of longifolene using acetic acid and sulphuric acid in dioxane. Alongwith isolongifolene, 3-sesquiterpene alcohols were also obtained as by-products. Typically, 200 g of longifolene in 500 mL acetic acid and 40 mL 50% sulphuric was stirred with 475 mL dioxane. The mixture was kept at 22–24° C. for 60 h followed by warming at 52° C. for 10 h and then poured into 600 mL water. The aqueous layer was treated with ammonium sulphates then extracted three times with 50 mL petroleum ether. The combined organic product was washed with water and dried to evaporate the solvent. This dried product has around 66% isolongifolene. The process has drawback of using many steps and large number of reagents, which are hazardous and toxic. This also has problem of disposal of spent reagent.
Wang, Hui, et. al., Jilin daxue Ziran Kexue Xuebao, 1, 88–90, 2001, (Chinese) wherein the isolation and identification of iso-longifolene alongwith other products from the volatile oil in the stems and leaves of panax ginseng have been reported. However, this is time-consuming process and it cannot meet the demand of large production, thereby necessitates the development of a synthetic route.